Image processing apparatus, image processing method, and computer program

ABSTRACT

An image processing apparatus includes: ΔΣ modulation means for applying, when predetermined signal processing is applied to a modulated image obtained by applying ΔΣ modulation to an image in a signal processing unit, the ΔΣ modulation to the image, wherein a frequency characteristic of noise shaping by the ΔΣ modulation is a characteristic opposite to a frequency characteristic of the predetermined signal processing.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationNo. JP 2008-272890 filed in the Japanese Patent Office on Oct. 23, 2008,the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing apparatus, an imageprocessing method, and a computer program, and, more particularly to animage processing apparatus, an image processing method, and a computerprogram for making it possible to improve, for example, whenpredetermined signal processing is applied to an image, the gradation ofan image obtained by the predetermined signal processing.

2. Description of the Related Art

FIG. 1 is a diagram of a configuration of an example of an imageprocessing system in the past (a system refers to a logical set ofplural apparatuses irrespective of whether the apparatuses havingindividual configurations are present in the same housing).

In FIG. 1, the image processing system includes an image-for-storagegenerating apparatus 10 and an image-for-display generating apparatus20.

The image-for-storage generating apparatus 10 includes a quantizationunit 11 and generates an image to be stored in the image-for-displaygenerating apparatus 20.

The image-for-display generating apparatus 20 can be applied to, forexample, a television receiver (hereinafter also referred to as TV(television)). The image-for-display generating apparatus 20 applied tothe TV stores, for example, an image of a menu screen and a backgroundimage as some kind of background. The image-for-storage generatingapparatus 10 generates an image stored by the image-for-displaygenerating apparatus 20.

Specifically, a multi-bit image such as an image including 16-bitcomponents of R, G, and B (Red, Green, and Blue) (hereinafter alsoreferred to as 16-bit image) created by, for example, a designer as anoriginal image of a menu screen using an image creation tool is suppliedto the image-for-storage generating apparatus 10.

In the image-for-storage generating apparatus 10, the quantization unit11 quantizes, for reduction of a volume and a calculation amount in theimage-for-display generating apparatus 20, the 16-bit image, which issupplied to the image-for-storage generating apparatus 10, into, forexample, 8 bits smaller than 16 bits. The image-for-storage generatingapparatus 10 outputs an 8-bit image (an image including 8-bit componentsof R, G, and B), which is obtained by the quantization in thequantization unit 11, in an image file of a format such as PNG (PortableNetwork Graphics).

The image-for-display generating apparatus 20 includes a storing unit21, a signal processing unit 22, and a gradation converting unit 23.

The storing unit 21 is, for example, a flash memory and stores the imagefile output by the image-for-storage generating apparatus 10.

Specifically, the image file output by the image-for-storage generatingapparatus 10 is written (stored) in the storing unit 21 in, for example,a factory that manufactures the TV to which the image-for-displaygenerating apparatus 20 is applied.

The signal processing apparatus 22 applies necessary signal processingto the 8-bit image of the menu screen stored in the image file stored inthe storing unit 21 and supplies an image subjected to the signalprocessing to the gradation converting unit 23.

The gradation converting unit 23 gradation-converts the image from thesignal processing unit 22 into the 8-bit image and supplies the 8-bitimage to, for example, a not-shown display that can display the 8-bitimage (hereinafter also referred to as 8-bit display).

Specifically, an image obtained as a result of the signal processingapplied to the 8-bit image by the signal processing unit 22 may be animage including a lager number of bits than the 8-bit image. It isdifficult to display the image including a larger number of bits thanthe 8-bit image on the 8-bit display. Therefore, the gradationconverting unit 23 gradation-converts the image from the signalprocessing unit 22 into the 8-bit image.

In the gradation converting unit 23, dithering processing for addingnoise to an image and then performing quantization of the image isperformed as gradation conversion. In this specification, the ditheringprocessing includes a dither method and an error diffusion method. Inthe dither method, noise unrelated to an image such as random noise isadded to the image and then quantization of the image is performed. Inthe error diffusion method, (a filtering result of) a quantization erroras noise is added to an image (error diffusion) and then quantization ofthe image is performed (see, for example, Hitoshi Tokay, “YokuwakaruDigital Image Processing”, sixth edition, CQ publishing).

The gradation converting unit 23 performs gradation conversion when theimage from the signal processing unit 22 is an image including a largernumber of bits than the 8-bit image. When the image from the signalprocessing unit 22 is the 8-bit image, the gradation converting unit 23directly supplies the 8-bit image to the 8-bit display.

The 8-bit image of the menu screen stored in the image file of thestoring unit 21 is processed as explained above and displayed on the8-bit display when, for example, a user performs operation to displaythe menu screen.

SUMMARY OF THE INVENTION

With the gradation conversion by the dithering processing in thegradation converting unit 23, it is possible to simulatively realizegradation equivalent to that of a multi-bit image making use of anintegral effect of human vision.

Specifically, for example, in the image-for-display generating apparatus20 shown in FIG. 1, concerning the menu screen, since the 8-bit image isstored in the image file of the storing unit 21, it is possible torealize gradation equivalent to that of the 8-bit image.

However, concerning the menu screen, it is difficult to realizegradation equivalent to that of the image including a larger number ofbits than the 8-bit image stored in the image file of the storing unit21.

Specifically, an original image of the menu screen is the 16-bit imagecreated by the designer. In the image-for-storage generating apparatus10, the 16-bit image as the original image is quantized into the 8-bitimage and stored in the storing unit 21 of the image-for-displaygenerating apparatus 20.

In the image-for-display generating apparatus 20, the 8-bit image of themenu screen stored in the storing unit is signal-processed by the signalprocessing unit 22, gradation-converted by the gradation converting unit23, and displayed.

In this way, the image of the menu screen is gradation-converted anddisplayed after the signal processing. However, in the image-for-displaygenerating apparatus 20, since the image as a target of the signalprocessing is the 8-bit image, it is difficult to realize, with thegradation conversion, an image having gradation exceeding that of the8-bit image.

Therefore, an image with gradation more substantially deteriorated thanan image intended by the designer is displayed as the menu screen.

Under the circumstances, it is desirable to make it possible to improve,when predetermined signal processing is applied to an image, thegradation of an image obtained by the predetermined signal processing.

According to an embodiment of the present invention, there is providedan image processing apparatus including ΔΣ modulation means forapplying, when predetermined signal processing is applied to a modulatedimage obtained by applying ΔΣ modulation to an image in a signalprocessing unit, the ΔΣ modulation to the image. A frequencycharacteristic of noise shaping by the ΔΣ modulation is a characteristicopposite to a frequency characteristic of the predetermined signalprocessing. According to the embodiment, there is also provided acomputer program for causing a computer to function as the imageprocessing apparatus.

According to another embodiment of the present invention, there isprovided an image processing method including the step of applying, whenpredetermined signal processing is applied to a modulated image obtainedby applying ΔΣ modulation to an image in a signal processing unit, theΔΣ modulation to the image. A frequency characteristic of noise shapingby the ΔΣ modulation is a characteristic opposite to a frequencycharacteristic of the predetermined signal processing.

In the embodiments of the present invention, when predetermined signalprocessing is applied to a modulated image obtained by applying the ΔΣmodulation to an image in the signal processing unit, the ΔΣ modulationis applied to the image. A frequency characteristic of the noise shapingby the ΔΣ modulation is a characteristic opposite to a frequencycharacteristic of the predetermined signal processing.

The image processing apparatus may be an independent apparatus or may bean internal block included in one apparatus.

It is possible to provide the computer program by transmitting thecomputer program via a transmission medium or recording the computerprogram on a recording medium.

According to the embodiments of the present invention, it is possible toimprove the gradation of an image. In particular, for example, when thepredetermined signal processing is applied to an image, it is possibleto improve the gradation of an image obtained by the predeterminedsignal processing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a configuration of an example of an imageprocessing system in the past;

FIG. 2 is a block diagram of a configuration example of an imageprocessing system according to an embodiment of the present invention;

FIG. 3 is a block diagram of a configuration example of ΔΣ modulationunit 31;

FIG. 4 is a block diagram of a configuration example of a filter 44;

FIG. 5 is a flowchart for explaining image processing performed by animage-for-storage generating apparatus 30;

FIG. 6 is a block diagram of a configuration example of a TV to which animage-for-display generating apparatus 20 is applied;

FIG. 7 is a block diagram of a configuration example of an imageprocessing apparatus to which an image-for-storage generating apparatus10 is applied;

FIGS. 8A and 8B are graphs representing images treated by an imageprocessing apparatus 70;

FIGS. 9A and 9B are graphs representing images treated by a TV 60;

FIGS. 10A and 10B are graphs representing content images;

FIG. 11 is a graph representing a combined image;

FIGS. 12A and 12B are graphs representing images after gradationconversion;

FIG. 13 is a block diagram of a configuration example of an imageprocessing apparatus to which the image-for-storage generating apparatus30 is applied;

FIG. 14 is a block diagram of a configuration example of a signalprocessing unit 62;

FIG. 15 is a graph of an amplitude characteristic of a LPF 92;

FIG. 16 is a graph of an amplitude characteristic of the LPF 92;

FIG. 17 is a graph of an amplitude characteristic of noise shaping by ΔΣmodulation;

FIG. 18 is a graph representing an image treated by an image processingapparatus 80;

FIGS. 19A to 19D are graphs representing images treated by the TV 60;and

FIG. 20 is a block diagram of a configuration example of a computeraccording to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An Overall ConfigurationExample of an Image Processing System According to an Embodiment of thePresent Invention

FIG. 2 is a diagram of a configuration example of an image processingsystem according to an embodiment of the present invention.

In the figure, components corresponding to those shown in FIG. 1 aredenoted by the same reference numerals. Explanation of the components isomitted below as appropriate.

The image processing system shown in FIG. 2 is the same as that shown inFIG. 1 in that the image processing system includes theimage-for-display generating apparatus 20. However, the image processingsystem shown in FIG. 2 is different from that shown in FIG. 1 in that animage-for-storage generating apparatus 30 is provided instead of theimage-for-storage generating apparatus 10 (FIG. 1).

The image-for-storage generating apparatus 30 includes a ΔΣ modulationunit 31.

For example, a 16-bit image created by a designer as an original imageof a menu screen is supplied to the image-for-storage generatingapparatus 30.

To reduce a volume and a calculation amount in the image-for-displaygenerating apparatus 20, the ΔΣ modulation unit 31 of theimage-for-storage generating apparatus 30 applies ΔΣ modulation, i.e.,gradation conversion by an error diffusion method to the 16-bit imagesupplied to the image-for-storage generating apparatus 30 and convertsthe 16-bit image into an 8-bit image.

In the ΔΣ modulation, noise as a quantization error of a pixel value ofa pixel spatially close to a pixel of attention, which is as a pixel towhich attention is paid for processing, is noise-shaped to a high bandof a spatial frequency in which the sensitivity of human vision is low.Error diffusion for adding the noise after noise shaping to the pixelvalue of the pixel of attention is performed. A pixel value after theaddition of the noise is quantized into 8 bits as a desired number ofbits.

As explained above, in the ΔΣ modulation, the pixel value to which thenoise (the quantization error) is added is quantized. Therefore, in theimage after the quantization (after gradation conversion), when lowerorder bits are simply truncated, it looks as if a pixel value in asection having a fixed value is subjected PWM (Pulse Width Modulation).As a result, it looks as if the gradation of the image after the ΔΣmodulation smoothly changes because of a spatial integral effect that anintegral in a spatial direction is performed in human vision. In otherwords, gradation equivalent to that of an original image (e.g., if theoriginal image is the 16-bit image as explained above, 2¹⁶ gradations)can be simulatively represented.

As explained in detail later, a frequency characteristic (an amplitudecharacteristic) of noise shaping by the ΔΣ modulation by the ΔΣmodulation unit 31 is a characteristic opposite to a frequencycharacteristic of signal processing (predetermined signal processing)performed by the signal processing unit 22 of the image-for-displaygenerating apparatus 20.

An image obtained by the ΔΣ modulation in the ΔΣ modulation unit 31 ishereinafter referred to as modulated image.

In the image-for-storage generating apparatus 30, the 8-bit image as themodulated image obtained by the ΔΣ modulation in the ΔΣ modulation unit31 is output as an image file of a format such as PNG.

The image file output by the image-for-storage generating apparatus 30is written in the storing unit 21 in a factory or the like thatmanufactures a TV to which the image-for-display generating apparatus 20is applied.

[A Configuration Example of the ΔΣ Modulation Unit 31]

FIG. 3 is a diagram of a configuration example of the ΔΣ modulation unit31 shown in FIG. 2.

In FIG. 3, the ΔΣ modulation unit 31 includes an arithmetic unit 41, aquantization unit 42, an arithmetic unit 43, and a filter 44.

The 16-bit image as the original image of the menu screen is supplied tothe arithmetic unit 41 as an image as a target of the ΔΣ modulation(hereinafter also referred to as target image). Further, output P of thefilter 44 that performs filtering in the spatial direction of aquantization error of a quantization value obtained by quantizing apixel value of the 16-bit image as the target image is supplied to thearithmetic unit 41.

The arithmetic unit 41 sets pixels of the target image as a pixel ofattention in raster scan order and adds up a 16-bit pixel value IN ofthe pixel of attention and the output P of the filter 44. The arithmeticunit 41 supplies (outputs) an added-up value U obtained as a result ofthe addition to the quantization unit 42 and the arithmetic unit 43.

The quantization unit 42 quantizes the added-up value U as the output ofthe arithmetic unit 41 into, for example, 8 bits smaller than 16 bits asthe number of bits of the target image. The quantization unit 42 outputsan 8-bit quantization value obtained as a result of the quantization asa modulated pixel value OUT, which is a result of the ΔΣ modulation ofthe pixel value IN.

The 8-bit modulated pixel value OUT output by the quantization unit 42is a pixel value of an 8-bit image as a modulated image. The 8-bitmodulated pixel value OUT output by the quantization unit 42 is suppliedto the arithmetic unit 43.

The arithmetic unit 43 calculates a difference U-OUT between theadded-up value U, which is the output of the arithmetic unit 41, and the8-bit modulated pixel value OUT as a quantized value of the added-upvalue U, which is the output of the quantization unit 42, to therebycalculate a quantization error Q included in the modulated pixel valueOUT as the quantized value and outputs the quantization error Q.

The quantization error Q output by the arithmetic unit 43 is supplied tothe filter 44.

The filter 44 is, for example, a FIR (Finite Impulse Response) filterthat performs filtering in two dimensions (the horizontal direction andthe vertical direction) of the spatial direction. The filter 44 performsfiltering in the spatial direction for the quantization error Q suppliedfrom the arithmetic unit 43. Further, the filter 44 supplies (outputs) aresult (P) of the filtering to the arithmetic unit 41.

When a transfer function of the filter 44 is represented as G, themodulated pixel value OUT output by the quantization unit 42 isrepresented by the following Formula (1):OUT=IN−(1−G)Q  (1)

In Formula (1), the quantization error Q is modulated by −(1−G). Themodulation by −(1−G) is noise shaping by the ΔΣ modulation in thespatial direction.

[A Configuration Example of the Filter 44]

FIG. 4 is a configuration example of the filter 44 shown in FIG. 3.

In FIG. 4, the filter 44 is a 12-tap two-dimensional FIR filter. Thefilter 44 includes twelve arithmetic units 51 _(1,3), 51 _(1,2), 51_(1,1), 51 _(2,3), 51 _(2,2), 51 _(2,1), 51 _(3,2), 51 _(3,1), 51_(4,1), 51 _(4,2), 51 _(5,1), and 51 _(5,2) and one arithmetic unit 52.

When a quantization error of a pixel xth from the left and yth from thetop among 5×5 pixels around a pixel of attention is represented asQ(x,y), the quantization error Q(x,y) is supplied to an arithmetic unit51 _(x,y).

Specifically, in FIG. 4, the quantization error Q(x,y) of each of twelvepixels processed (set as a pixel of attention) earlier than the pixel ofattention in raster scan order among the 5×5 pixels around the pixel ofattention is supplied to the arithmetic unit 51 _(x,y).

The arithmetic unit 51 _(x,y) multiplies together the quantization errorQ(x,y) supplied thereto and a filter coefficient a(x,y) set in advanceand supplies a multiplied value obtained as a result of themultiplication to the arithmetic unit 52.

The arithmetic unit 52 adds up multiplied values supplied from thetwelve arithmetic units 51 _(x,y) and outputs an added-up value P of themultiplied values to the arithmetic unit 41 (FIG. 3) as a filteringresult of the quantization error.

In the arithmetic unit 41 shown in FIG. 3, the filtering result obtainedby using the quantization errors Q(x,y) of the twelve pixels processedearlier than the pixel of attention in raster scan order among the 5×5pixels around the pixel of attention as explained above is added to thepixel value IN of the pixel of attention.

[Processing by the Image-for-Storage Generating Apparatus 30]

Image processing (image-for-storage generation processing) performed bythe image-for-storage generating apparatus 30 shown in FIG. 2 isexplained with reference to FIG. 5.

The image-for-storage generating apparatus 30 waits for a certain frame(for one screen) of the 16-bit image to be supplied thereto and receivesthe frame. In step S10, the image-for-storage generating apparatus 30performs the ΔΣ modulation with the 16-bit image set as a target imageand outputs an 8-bit image obtained as a result of the ΔΣ modulation asa modulated image.

Specifically, in the ΔΣ modulation unit 31 (FIG. 3) of theimage-for-storage generating apparatus 30, the arithmetic unit 41 waitsfor a certain frame of the target image to be supplied and receives theframe. The arithmetic unit 41 sets a pixel, which is not set as a pixelof attention yet in raster scan order among pixels of the frame, as apixel of attention. In step S11, the arithmetic unit 41 adds up a pixelvalue of the pixel of attention and a value (output of the filter 44)obtained by filtering in step S14 explained later performed by thefilter 44 immediately before. The arithmetic unit 41 outputs an added-upvalue obtained as a result of the addition to the quantization unit 42and the arithmetic unit 43. The processing proceeds to step S12.

In step S12, the quantization unit 42 quantizes the added-up value,which is the output of the arithmetic unit 41, and outputs a quantizedvalue including a quantization error as a modulated pixel value of apixel in the position of the pixel of attention of the modulated image.The processing proceeds to step S13.

The modulated pixel value as the quantized value output by thequantization unit 42 is supplied to the arithmetic unit 43.

In step S13, the arithmetic unit 43 calculates a difference between theadded-up value as the output of the arithmetic unit 41 and the output ofthe quantization unit 42 (the quantized value of the added-up value asthe output of the arithmetic unit 41) (the modulated pixel value) tothereby calculate a quantization error due to the quantization by thequantization unit 42. Further, the arithmetic unit 43 supplies thequantization error to the filter 44. The processing proceeds from stepS13 to step S14.

In step S14, the filter 44 performs filtering in the spatial directionof the quantization error supplied from the arithmetic unit 43 andsupplies (outputs) a result of the filtering to the arithmetic unit 41.

Thereafter, the arithmetic unit 41 sets the next pixel of the pixel ofattention as a new pixel of attention in raster scan order. Theprocessing returns from step S14 to step S11. The arithmetic unit 41adds up a pixel value of the new pixel of attention and the filteringresult supplied from the filter 44 in the immediately preceding stepS14. The same processing is repeated.

The processing from steps S11 to S14 is repeatedly performed until thesupply of the 16-bit image to the image-for-storage generating apparatus30 is stopped.

[A Configuration Example of a TV to which the Image-for-DisplayGenerating Apparatus 20 is Applied]

The image-for-display generating apparatus 20 shown in FIG. 2 (andFIG. 1) can be applied to an apparatus that treats an image such as aTV.

FIG. 6 is a diagram of a configuration example of the TV to which theimage-for-display generating apparatus 20 shown in FIG. 2 is applied.

In FIG. 6, the TV 60 includes a storing unit 61, a signal processingunit 62, a gradation converting unit 63, and a blending unit 64.

The storing unit 61 corresponds to the storing unit 21 shown in FIG. 2.The storing unit 61 stores, for example, an image file in which an 8-bitimage as a modulated image obtained by applying the ΔΣ modulation to the16-bit image created by the designer as the original image of the menuscreen is stored.

The signal processing unit 62 corresponds to the signal processing unit22 shown in FIG. 2. The signal processing unit 62 applies necessarysignal processing to the 8-bit image of the menu screen stored in theimage file of the storing unit 61 and supplies the 8-bit image to theblending unit 64.

The 8-bit image stored in the image file of the storing unit 61 is, forexample, an image half as large as the 16-bit image as the originalimage of the menu screen in both horizontal and vertical sizes.

Therefore, the signal processing unit 62 applies, as signal processing,expansion processing for expansion at an expansion ratio 2 to the 8-bitimage of the menu screen stored in the image file of the storing unit 61to obtain an 8-bit image having the same size as the original image andsupplies the 8-bit image to the blending unit 64.

The gradation converting unit 63 corresponds to the gradation convertingunit 23 shown in FIG. 2. The gradation converting unit 63gradation-converts a combined image explained later from the blendingunit 64 into an 8-bit image, supplies the 8-bit image to a not-shown8-bit display, and causes the 8-bit display to display the 8-bit image.

The blending unit 64 combines the 8-bit image of the menu screensupplied from the signal processing unit 62 and an image of a program ofa television broadcast or the like (hereinafter also referred to ascontent image) to generate a combined image and supplies the combinedimage to the gradation converting unit 63.

The blending unit 64 includes arithmetic units 65, 66, and 67 andperforms so-called a blending using a predetermined coefficient α.

The 8-bit image of the menu screen from the signal processing unit 62 issupplied to the arithmetic unit 65. The arithmetic unit 65 multipliesthe 8-bit image of the menu screen from the signal processing unit 62with the coefficient α (α is a value in a range of 0 to 1) for the αblending and supplies a multiplied value obtained as a result of themultiplication to the arithmetic unit 67.

A content image is supplied to the arithmetic unit 66 from a not-showntuner or the like. The arithmetic unit 66 multiplies the content imagewith a coefficient 1−α and supplies a multiplied value obtained as aresult of the multiplication to the arithmetic unit 67.

The arithmetic unit 67 adds up the multiplied value from the arithmeticunit 65 and the multiplied value from the arithmetic unit 66 to therebygenerate a combined image obtained by superimposing the menu screen onthe content image and supplies the combined image to the gradationconverting unit 63.

In the TV 60 configured as explained above, the signal processing unit62 applies, as signal processing, the expansion processing for expansionat an expansion ratio 2 to the 8-bit image of the menu screen stored inthe image file of the storing unit 61 to obtain an 8-bit image havingthe same size as the original image and supplies the 8-bit image to theblending unit 64.

In the blending unit 64, the arithmetic unit 65 multiplies the 8-bitimage of the menu screen from the signal processing unit 62 with thecoefficient α and supplies a multiplied value obtained as a result ofthe multiplication to the arithmetic unit 67. Further, the arithmeticunit 66 multiplies the content image with the coefficient 1−α andsupplies a multiplied value obtained as a result of the multiplicationto the arithmetic unit 67. The arithmetic unit 67 adds up the multipliedvalue from the arithmetic unit 65 and the multiplied value from thearithmetic unit 66 to thereby generate a combined image and supplies thecombined image to the gradation converting unit 63.

The gradation converting unit 63 gradation-converts the combined imagefrom the blending unit 64 into an 8-bit image, supplies the 8-bit imageto the not-shown 8-bit display, and causes the 8-bit display to displaythe 8-bit image.

[A Configuration Example of the Image Processing Apparatus to which theImage-for-Storage Generating Apparatus 10 is Applied]

When, as explained above, the 8-bit image half as large as the 16-bitimage as the original image of the menu screen (or the image file inwhich the 8-bit image is stored) is stored in the storing unit 61 of theTV 60 to which the image-for-display generating apparatus 20 is applied,an image processing apparatus to which the image-for-storage generatingapparatus 10 is applied generates such an 8-bit image. The imageprocessing apparatus is explained below.

FIG. 7 is a diagram of a configuration example of the image processingapparatus to which the image-for-storage generating apparatus 10 shownin FIG. 1 is applied.

In FIG. 7, an image processing apparatus 70 includes a reducing unit 71and a quantization unit 72.

The 16-bit image as the original image of the menu screen is supplied tothe reducing unit 71. The reducing unit 71 reduces the size of the16-bit image as the original image of the menu screen according to areduction ratio 1/2 corresponding to the expansion ratio of theexpansion processing in the signal processing unit 62 (FIG. 6). Thereducing unit 70 outputs a 16-bit reduced image (a reduced imageincluding 16-bit components of R, G, and B) obtained by the reduction ofthe size to the quantization unit 72.

The quantization unit 72 corresponds to the quantization unit 11 shownin FIG. 1. The quantization unit 72 quantizes the 16-bit reduced imagefrom the reducing unit 71 into 8 bits.

The image processing apparatus 70 stores an 8-bit reduced image obtainedby the quantization in the quantization unit 72 in an image file andoutputs the 8-bit reduced image.

[Images Treated by the Image Processing Apparatus 70 and Images Treatedby the TV 60 when the 8-Bit Reduced Image Obtained by the ImageProcessing Apparatus 70 is Stored in the TV 60]

Images treated by the image processing apparatus 70 shown in FIG. 7 andimages treated by the TV 60 when the 8-bit reduced image obtained by theimage processing apparatus 70 is stored in the storing unit 61 of the TV60 (FIG. 6) are explained below.

FIGS. 8A and 8B are graphs representing images treated by the imageprocessing apparatus 70 shown in FIG. 7.

In FIGS. 8A and 8B (and FIGS. 9A and 9B to FIGS. 12A and 12B, FIG. 18,and FIGS. 19A to 19D referred to later), the abscissa representspositions of pixels arranged in the horizontal direction (or thevertical direction) and the ordinate represents pixel values.

FIG. 8A is a graph representing a 16-bit reduced image obtained byreducing the size of the 16-bit image as the original image of the menuscreen to a half in the reducing unit 71 (FIG. 7).

In the 16-bit reduced image in FIG. 8A, pixel values of first pixel to a200th pixel from the left smoothly (linearly) change from 100 to 110.

FIG. 8B is a graph representing an 8-bit reduced image obtained byquantizing the 16-bit reduced image in FIG. 8A into 8 bits in thequantization unit 72 (FIG. 7).

In the 8-bit reduced image in FIG. 8B, pixel values from a first pixelto a 200th pixel from the left change stepwise from 100 to 110. Thegradation of the 8-bit reduced image lowers compared with the 16-bitreduced image in FIG. 8A because of the quantization by the quantizationunit 72. Specifically, the 8-bit reduced image shown in FIG. 8B ischanged to an image having 2⁸ gradations by the quantization by thequantization unit 72.

FIGS. 9A and 9B are graphs representing images treated by the TV 60 whenthe 8-bit reduced image shown in FIG. 8B is stored in the storing unit61 of the TV 60 shown in FIG. 6.

Specifically, FIG. 9A is a graph representing an image having size sameas the size of the original image of the menu screen (hereinafter alsoreferred to as original size image) obtained by expanding the size ofthe 8-bit reduced image in FIG. 8B to double size in the signalprocessing unit 62 (FIG. 6).

In the original size image in FIG. 9A, pixel values of a first pixel toa 400th pixel from the left in a range twice as large as the range ofthe first pixel to the 200th pixel from the left change stepwise from100 to 109. As in the case of FIG. 8B, the gradation of the image lowerscompared with the 16-bit reduced image shown in FIG. 8A because of thequantization by the quantization unit 72.

FIG. 9B is a graph representing an image obtained by multiplying theoriginal size image in FIG. 9A with the coefficient α (hereinafter alsoreferred to as α-times image) in the arithmetic unit 65 (FIG. 6).

Specifically, FIG. 9B represents the α-times image obtained by thearithmetic unit 65 when the coefficient α is set to, for example, 0.5.

In the α-times image in FIG. 9B, pixel values of a first pixel to a400th pixel from the left change stepwise from 50 to 54.5, which are 0.5(=a) times as large as 100 to 109 in the case of FIG. 9A. As in the caseof FIG. 8B and FIG. 9A, the gradation of the image lowers.

FIGS. 10A and 10B are graphs representing content images.

Specifically, FIG. 10A is a graph representing a content image suppliedto the arithmetic unit 66 (FIG. 6).

In the content image in FIG. 10A, pixel values of a first pixel to 400thpixel from the left are a fixed value 60.

FIG. 10B is a graph representing an image obtained by multiplying thecontent image in FIG. 10A with the coefficient 1−α (hereinafter alsoreferred to as 1−α-times image) in the arithmetic unit 66 (FIG. 6).

Specifically, FIG. 10B represents the 1−α-times image obtained by thearithmetic unit 66 when the coefficient α is set to 0.5 as explainedwith reference to FIGS. 9A and 9B.

In the 1−α-times image in FIG. 10B, pixel values of a first pixel to a400th pixel from the left are 30 that is 0.5 (=1−α) times as large as 60in the case of FIG. 10A.

FIG. 11 is a graph representing a combined image obtained by performingthe a blending (combination) of the α-times image in FIG. 9B and the1−α-times image in FIG. 10B in the arithmetic unit 67 (FIG. 6).

In the combined image in FIG. 11, the α-times image in FIG. 9B in whichthe pixel values of the first pixel to the 400th pixel from the leftchange stepwise from 50 to 54.5 and the 1−α-times image in FIG. 10B inwhich the pixel values of the first pixel to the 400th pixel from theleft are 30 are added up. Therefore, in the combined image, pixel valuesof a first pixel to a 400th pixel from the left change stepwise from 80to 84.5. As in the cases of FIG. 8B and FIG. 9A, the gradation of thecombined image lowers.

FIGS. 12A and 12B are graphs representing images after gradationconversion (hereinafter also referred to as post-gradation conversionimage) obtained by gradation-converting the combined image in FIG. 11into 8 bits.

Specifically, FIG. 12A is a graph representing a post-gradationconversion image obtained when the combined image in FIG. 11 isgradation-converted into 8 bits only by quantization in the gradationconverting unit 63 (FIG. 6).

In the post-gradation conversion image in FIG. 12A, pixel values of afirst pixel to a 400th pixel from the left change stepwise at a largerstep from 80 to 85. The gradation of the post-gradation conversion imagelowers more than those in the case of FIG. 11.

Specifically, the α-times image in FIG. 9B used for the generation ofthe combined image is an image obtained by multiplying the original sizeimage in FIG. 9A with 0.5 (=2⁻¹) as the coefficient α. When such anα-times image (or the combined image generated by using the α-timesimage) is gradation-converted into 8 bits only by quantization, theα-times image is substantially converted into an image having 2⁷gradations. Therefore, the gradation lowers below that before thegradation conversion.

FIG. 12B is a graph representing a post-gradation conversion imageobtained when the combined image in FIG. 11 is gradation-converted into8 bits by the dithering processing in the gradation converting unit 63(FIG. 6).

In the post-gradation conversion image in FIG. 12B, pixel values changeas if the pixel values are subjected to the PWM. It looks as if thepixel values changing in that way smoothly change because of the spatialintegral effect of vision.

Specifically, in the post-gradation conversion image in FIG. 12B,concerning an image of the menu screen, gradation equivalent to that ofthe 8-bit reduced image stored in the storing unit 61 (FIG. 6) issimulatively realized.

However, in the post-gradation conversion image in FIG. 12B, the imageof the menu screen is not an image having gradation equivalent to thatof the 16-bit image as the original image of the menu screen.

As explained above, in the arithmetic unit 65 (FIG. 6), the originalsize image in FIG. 9A in which the pixel values change from 100 to 109is multiplied with a (=0.5) to be the α-times image in FIG. 9B in whichthe pixel values change from 50 to 54.5.

Therefore, in the α-times image in FIG. 9B, the change in the pixelvalues is gentler than that of the original size image in FIG. 9A.Therefore, banding is more conspicuous in a combined image aftergradation conversion obtained by gradation-converting such an α-timesimage (or the combined image generated by using the α-times image).

Specifically, in the combined image after gradation conversion of theimage in which the change in the pixel values is gentle, a section inwhich fixed pixel values continue long increases. Therefore, banding inwhich a change in gradation looks like a band is conspicuous.

[A Configuration Example of an Image Processing Apparatus to Which theImage-for-Storage Generating Apparatus 30 is Applied]

In the post-gradation conversion image, to simulatively change the imageof the menu screen to an image having gradation equivalent to that ofthe 16-bit image as the original image of the menu screen and to animage in which banding is not conspicuous, the image as the target ofgradation conversion, i.e., the combined image obtained by the blendingunit 64 (FIG. 6) needs to be the image having gradation equivalent tothat of the 16-bit image.

FIG. 13 is a diagram of a configuration example of an image processingapparatus to which the image-for-storage generating apparatus 30 shownin FIG. 2 is applied.

In the figure, components corresponding to those of the image processingapparatus 70 shown in FIG. 7 are denoted by the same reference numerals.Explanation of the components is omitted below as appropriate.

Specifically, in FIG. 13, an image processing apparatus 80 includes thereducing unit 71 and a ΔΣ modulation unit 81. The image processingapparatus 80 is the same as the image processing apparatus 70 shown inFIG. 7 in that the image processing apparatus 80 includes the reducingunit 71. The image processing apparatus 80 is different from the imageprocessing apparatus 70 shown in FIG. 7 in that the ΔΣ modulation unit81 is provided instead of the quantization unit 72.

A 16-bit reduced image obtained by reducing the size of the 16-bit imageas the original image of the menu screen at a reduction ratio 1/2corresponding to the expansion ratio of the expansion processing in thesignal processing unit 62 (FIG. 6) in the reducing unit 71 is suppliedto the ΔΣ modulation unit 81.

The ΔΣ modulation unit 81 corresponds to the ΔΣ modulation unit 31 shownin FIG. 2. The ΔΣ modulation unit 81 applies the ΔΣ modulation to the16-bit reduced image supplied from the reducing unit 71 and converts the16-bit reduced image into an 8-bit reduced image.

The image processing apparatus 80 stores the 8-bit reduced imageobtained by the ΔΣ modulation by the ΔΣ modulation unit 81 in an imagefile and outputs the 8-bit reduced image.

[A Frequency Characteristic of the Noise Shaping by the ΔΣ Modulation]

A frequency characteristic of the noise shaping by the ΔΣ modulation bythe ΔΣ modulation unit 81 shown in FIG. 13 is a characteristic oppositeto a frequency characteristic of signal processing performed by thesignal processing unit 62 of the TV 60 (FIG. 6).

Therefore, to explain the frequency characteristic of the noise shapingby the ΔΣ modulation by the ΔΣ modulation unit 81, the frequencycharacteristic of the signal processing performed by the signalprocessing unit 62 is explained.

As explained with reference to FIG. 6, in the TV 60, the signalprocessing unit 62 applies, as signal processing, expansion processingfor expansion at an expansion ratio 2 to the 8-bit image (the 8-bitreduced image) of the menu screen stored in the image file of thestoring unit 61.

FIG. 14 is a diagram of a configuration example of the signal processingunit 62 that performs such expansion processing as signal processing.

In FIG. 14, the signal processing unit 62 includes an up-sampling unit91 and a LPF (Low Pass Filter) 92.

The 8-bit reduced image of the menu screen stored in the image file ofthe storing unit 61 (FIG. 6) is supplied to the up-sampling unit 91.

The up-sampling unit 91 interpolates pixels having pixel values 0 one byone among adjacent pixels forming the 8-bit reduced image to therebygenerate an 8-bit image having a double size and supplies the 8-bitimage to the LPF 92.

Specifically, the up-sampling unit 91 generates, according to theinterpolation of the zero value, an image in which both the numbers ofhorizontal and vertical pixels are twice as large as those of the 8-bitreduced image and supplies the image to the LPF 92.

The LPF 92 filters the image supplied from the up-sampling unit 91 tothereby, for example, linearly interpolate the pixel values of thepixels in which the zero value is interpolated by the up-sampling unit91. The LPF 92 supplies an image having a size same as that of theoriginal image of the menu screen (an original size image) obtained as aresult of the linear interpolation to the blending unit 64 (FIG. 6).

As explained above, the signal processing unit 62 interpolates the zerovalue in the 8-bit reduced image and performs the filtering with the LPF92 to thereby perform expansion processing for expanding an image at anexpansion ratio 2 (resizing processing for resetting the reduce image tothe original size).

To simplify the explanation, attention is paid to only the horizontaldirection of the 8-bit reduced image. The up-sampling unit 91interpolates pixels having pixel values 0 one by one among pixelsadjacent to one another in the horizontal direction to of the 8-bitreduced image thereby generate an image having a double size in thehorizontal direction.

The up-sampling unit 91 doubles the pixel values of the pixels havingthe double size in the horizontal direction to prevent an average of thepixel values from changing and supplies the pixel values to the LPF 92.

The LPF 92 is a FIR filter in which, for example, filter coefficientsfor multiplying (pixel values of) three pixels continuous in thehorizontal direction are 1/4, 1/2, and 1/4. The LPF 92 filters the imagesupplied from the up-sampling unit 91 in the horizontal direction.Consequently, the original size image obtained by linearly interpolatingthe pixel values of the pixels interpolated by the up-sampling unit 91is output from the LPF 92.

When the signal processing unit 62 includes the up-sampling unit 91 andthe LPF 92 as explained above, the frequency characteristic of the noiseshaping by the ΔΣ modulation by the ΔΣ modulation unit 81 (FIG. 13) is acharacteristic opposite to the frequency characteristic of the LPF 92.

FIG. 15 is a graph of a frequency characteristic (an amplitudecharacteristic) of the LPF 92.

In FIG. 15 (and FIG. 16 referred to later), the abscissa represents afrequency with a half of a sampling frequency of pixels of an image (animage in which the zero value is interpolated) as a target of filteringby the LPF 92 normalized to 1 (hereinafter also referred to asnormalized frequency). The ordinate represents a gain in a unit of dB.

The ΔΣ modulation unit 81 (FIG. 13) performs the ΔΣ modulation targetingthe 8-bit reduced image having a size half as large as the size of theimage (the image in which the zero value is interpolated) as the targetof the filtering by the LPF 92 (hereinafter also referred to aszero-interpolated image).

A sampling frequency of the pixels of the 8-bit reduced image as thetarget of the ΔΣ modulation is a half of a sampling frequency of thepixels of the zero-interpolated image as the target of the filtering bythe LPF 92.

Therefore, concerning the 8-bit reduced image as the target of the ΔΣmodulation, since a portion having a normalized frequency equal to orlower than 0.5 in the frequency characteristic of the LPF 92 affects thefiltering by the LPF 92, only that portion has to be taken into account.

FIG. 16 is a graph of the portion having the normalized frequency equalto or lower than 0.5 in the frequency characteristic of the LPF 92 shownin FIG. 15.

The frequency characteristic of the noise shaping by the ΔΣ modulationby the ΔΣ modulation unit 81 (FIG. 13) is a characteristic opposite tothe frequency characteristic shown in FIG. 16.

FIG. 17 is a graph of a frequency characteristic (an amplitudecharacteristic) of the noise shaping by the ΔΣ modulation by the ΔΣmodulation unit 81 (FIG. 13).

In FIG. 17, the abscissa represents a frequency with a half of asampling frequency of pixels of an 8-bit reduced image as a target ofthe ΔΣ modulation normalized to 1 (a normalized frequency). The ordinaterepresents a gain in a unit of dB.

A normalized frequency 1 in FIG. 17 corresponds to the normalizedfrequency 0.5 of the frequency characteristic of the LPF 92 (FIG. 14)shown in FIGS. 15 and 16.

The frequency characteristic of the noise shaping shown in FIG. 17 is acharacteristic that, when the normalized frequency is 0, a gain is 0and, as the normalized frequency is in a higher band (a higher band of aspatial frequency), a gain is larger. The frequency characteristic is(substantially) opposite to the frequency characteristic shown in FIG.16.

The frequency characteristic of the noise shaping does not need tocompletely coincide with an opposite characteristic obtained byreversing the frequency characteristic of the signal processing unit 62(FIG. 6), namely here, the frequency characteristic of the LPF 92 (FIG.14) (the portion having the normalized frequency equal to or lower than0.5 (FIG. 16)).

According to the frequency characteristic shown in FIG. 16, concerningthe 8-bit reduced image as the target of the ΔΣ modulation, ahigh-frequency component of the spatial frequency is attenuated by thefiltering by the LPF 92.

The ΔΣ modulation unit 81 (FIG. 13) adds a high-frequency noise (aquantization error) attenuated (averaged) by the filtering by the LPF 92to perform the ΔΣ modulation such that the original size image obtainedby the filtering by the LPF 92 is an image having gradation equivalentto that of the 16-bit image.

Therefore, the frequency characteristic of the noise shaping by the ΔΣmodulation only has to be a characteristic that noise (a quantizationerror) corresponding to the frequency characteristic is attenuated(ideally, completely) by the filtering by the LPF 92.

In other words, the frequency characteristic of the noise shaping by theΔΣ modulation only has to be a characteristic of a shape similar to ashape obtained by reversing the frequency characteristic of the LPF 92(the portion having the normalized frequency equal to or lower than 0.5(FIG. 16)).

In this specification, when the frequency characteristic of the noiseshaping is a characteristic opposite to the frequency characteristic ofthe signal processing unit 62 (FIG. 6), this means that the frequencycharacteristic of the noise shaping completely coincides with thecharacteristic opposite to the frequency characteristic of the signalprocessing by the signal processing unit 62. Besides, this also meansthat the frequency characteristic of the noise shaping is similar to theopposite characteristic.

The ΔΣ modulation unit 81 is configured the same as the ΔΣ modulationunit 31 shown in FIG. 3. However, the frequency characteristic of thenoise shaping by the ΔΣ modulation by the ΔΣ modulation unit 81 dependson a transfer function G of the filter 44 (FIG. 3) and a filtercoefficient of the filter 44.

For example, as explained above, the signal processing by the signalprocessing unit 62 (FIG. 6) is expansion processing for expanding thesize of an image to double size with linear interpolation and the filter44 is the 12-tap two-dimensional FIR filter as shown in FIG. 4. In thiscase, the filter coefficient a(x,y) (FIG. 4) of the filter 44 forsetting the frequency characteristic of the noise shaping by the ΔΣmodulation by the ΔΣ modulation unit 81 to the characteristic oppositeto the frequency characteristic of the signal processing by the signalprocessing unit 62 is, for example, as follows:

a(1,1)=−0.0064

a(2,1)=−0.0256

a(3,1)=−0.0384

a(4,1)=−0.0256

a(5,1)=−0.0064

a(1,2)=−0.0256

a(2,2)=0.1816

a(3,2)=0.4144

a(4,2)=0.1816

a(5,2)=−0.0256

a(1,3)=−0.0384

a(2,3)=0.4144

[Images Treated by the Image Processing Apparatus 80 and Images Treatedby the TV 60 when an 8-Bit Reduced Image Obtained by the ImageProcessing Apparatus 80 is Stored in the TV 60]

Images treated by the image processing apparatus 80 shown in FIG. 13 andimages treated by the TV 60 when an 8-bit reduced image obtained by theimage processing apparatus 80 is stored in the storing unit 61 of the TV60 (FIG. 6) are explained below.

FIG. 18 is a graph representing an image treated by the image processingapparatus 80 shown in FIG. 13.

Specifically, FIG. 18 represents an 8-bit reduced image as a modulatedimage obtained by applying the ΔΣ modulation to the 16-bit reduced imagein FIG. 8A obtained by the reducing unit 71 in the ΔΣ modulation unit 81(FIG. 13).

In the 8-bit reduced image as the modulated image in FIG. 18, pixelvalues change as if the pixel values are subjected to the PWM. It looksas if the pixel values changing in that way smoothly change because ofthe spatial integral effect of vision.

Specifically, in the 8-bit reduced image as the modulated image in FIG.18, gradation equivalent to that of the 16-bit reduced image (FIG. 8A)before being subjected to the ΔΣ modulation is simulatively realized.

FIGS. 19A to 19D are graphs representing images treated by the TV 60when the 8-bit reduced image in FIG. 18 is stored in the storing unit 61of the TV 60 shown in FIG. 6.

In FIGS. 19A to 19D, pixel values of a first pixel to a 400th pixel fromthe left are shown.

FIG. 19A is a graph representing the size of an original size imageobtained by expanding the 8-bit reduced image in FIG. 18 to double sizein the signal processing unit 62 (FIG. 6).

As explained above, in the signal processing unit 62 (FIG. 14), thesignal processing as the expansion processing for interpolating the zerovalue and performing the filtering by the LPF 92 is performed. The noise(the quantization error) having the characteristic opposite to thefrequency characteristic of the LPF 92 is added to the 8-bit reducedimage in FIG. 18 (the ΔΣ modulation for performing the noise shaping ofthe frequency characteristic opposite to the frequency characteristic ofthe LPF 92 is applied to the 8-bit reduced image).

Therefore, when the signal processing as the expansion processing by thesignal processing unit 62 is applied to the 8-bit reduced image in FIG.18, the noise added to the reduced image is attenuated (averaged). As aresult, the original size image obtained by the signal processing as theexpansion processing by the signal processing unit 62 is an imageobtained by, so to speak, restoring the 16-bit image (the original imageof the menu screen) simulatively realized by the spatial integral effectof vision.

FIG. 19B is a graph representing a combined image obtained by settingthe coefficient α to, for example, 0.5 and adding up an image obtainedby multiplying the original size image in FIG. 19A with the coefficientα (an α-times image) and the 1−α-times image in FIG. 10B in the blendingunit 64 (FIG. 6).

It is seen that the combined image in FIG. 19B is an image having a highgradation compared with the combined image in FIG. 11.

FIG. 19C is a graph representing, so to speak, an ideal combined imageobtained by setting the coefficient α to 0.5 and performing the ablending of an image obtained by multiplying the 16-bit image as theoriginal image of the menu screen with the coefficient α (an α-timesimage) and the 1−α-times image in FIG. 10B.

The combined image in FIG. 19B is an image having gradation closer (moresimilar) to that of the ideal combined image in FIG. 19C than thegradation of the combined image in FIG. 11.

FIG. 19D is a graph representing a post-gradation conversion imageobtained by gradation-converting the combined image in FIG. 19B into 8bits with the dithering processing in the gradation converting unit 63(FIG. 6).

In the post-gradation conversion image in FIG. 19D, pixel values changeas if the pixel values are subjected to the PWM. It looks as if thepixel values changing in that way smoothly change because of the spatialintegral effect of vision.

Specifically, the combined image as the target of the gradationconversion by the dithering processing in the gradation converting unit63 (FIG. 6) is, as shown in FIG. 19B, the image close to the idealcombined image in FIG. 19C and has gradation close to that of the idealcombined image.

In the post-gradation conversion image obtained by performing thedithering processing of such a combined image, gradation equivalent tothat of the combined image before the gradation conversion issimulatively realized (by the spatial integral effect of vision).

Specifically, in the post-gradation conversion image in FIG. 19D,concerning an image of the menu screen, gradation substantiallyequivalent to that of the 16-bit image as the original image of the menuscreen is simulatively realized.

Therefore, in the TV 60 (FIG. 6), when the expansion processing isapplied to the image of the menu screen as predetermined signalprocessing, the gradation of an image obtained by the expansionprocessing as the predetermined signal processing can be improved.

The combined image as the target of the gradation conversion by thedithering processing in the gradation converting unit 63 (FIG. 6) has,as shown in FIG. 19B, the gradation close to that of the ideal combinedimage in FIG. 19C. Therefore, in an image obtained bygradation-converting the combined image, banding can be prevented fromoccurring compared with the image obtained by gradation-converting thecombined image in which pixel values change stepwise shown in FIG. 11.

As explained above, the ΔΣ modulation, the frequency characteristic ofthe noise shaping by which is the characteristic opposite to thefrequency characteristic of the signal processing by the signalprocessing unit 62 of the TV (FIG. 6), is applied to the 16-bit reducedimage obtained by reducing the original image of the menu screen togradation-convert the 16-bit reduced image into an 8-bit reduced imageas a modulated image and store the 8-bit reduced image in the TV 60.This allows the TV 60 to display an image of a menu screen having a highgradation close to that of the original image of the menu screen withoutproviding special hardware or software.

The image processing apparatus 80 (FIG. 13) can set, besides an image asa UI (User Interface) such as the image (the original image) of the menuscreen, a photographed image of a real world and the like as aprocessing target.

The image processing apparatus 80 can set both a still image and amoving image as processing targets.

The expansion processing as the signal processing by the signalprocessing unit 62 of the TV 60 (FIG. 6) can be performed by, besidesthe linear interpolation, nearest neighbor interpolation, cubicinterpolation, and the like.

As the expansion processing by the signal processing unit 62, processingfor expanding an image at an expansion ratio other than 2 can beadopted.

The signal processing by the signal processing unit 62 is not limited tothe expansion processing.

[A Configuration Example of a Computer According to an Embodiment of thePresent Invention]

The series of processing explained above can be performed by hardwareand can be performed by software. When the series of processing isperformed by software, a computer program configuring the software isinstalled in a general-purpose computer or the like.

FIG. 20 is a diagram of a configuration example of a computer accordingto an embodiment of the present invention in which the computer programfor executing the series of processing is installed.

The computer program can be recorded in advance on a hard disk 105 and aROM (Read Only Memory) 103 as recording media incorporated in thecomputer.

Alternatively, the computer program can be temporarily or permanentlystored (recorded) on a removable recording medium 111 such as a flexibledisk, a CD-ROM (Compact Disc Read Only Memory), an MO (Magneto Optical)disk, a DVD (Digital Versatile Disc), a magnetic disk, or asemiconductor memory. Such a removable recording medium 111 can beprovided as so-called package software.

Besides being installed in the computer from the removable recordingmedium 111 explained above, the computer program can be transferred froma download site to the computer by radio via an artificial satellite fora digital satellite broadcast or can be transferred to the computer bywire via a network such as a LAN (Local Area Network) or the Internet.The computer can receives the computer program transferred in that wayin a communication unit 108 and install the computer program in the harddisk 105 incorporated therein.

The computer incorporates a CPU (Central Processing Unit) 102. An inputand output interface 110 is connected to the CPU 102 via a bus 101.When, for example, a user operates an input unit 107 including akeyboard, a mouse, and a microphone to input a command via the input andoutput interface 110, the CPU 102 executes the computer program storedin the ROM (Read Only Memory) 103 according to the command. The CPU 102loads the computer program stored in the hard disk 105, the computerprogram transferred from the satellite or the network, received by thecommunication unit 108, and installed in the hard disk 105, or thecomputer program read out from the removable recording medium 111, whichis inserted in a drive 109, and installed in the hard disk 105 to a RAM(Random Access Memory) 104 and executes the computer program.Consequently, the CPU 102 performs processing conforming to theflowcharts explained above or processing performed by the componentsshown in the block diagrams explained above. For example, the CPU 102outputs a result of the processing from an output unit 106 including anLCD (Liquid Crystal Display) or a speaker or transmits the processingresult from the communication unit 108 via the input and outputinterface 110 or causes the hard disk 105 to record the processingresult according to necessity.

In this specification, processing steps describing a computer programfor causing the computer to execute various kinds of processing do notalways have to be processed in time series according to the orderdescribed as the flowcharts and include processing executed in parallelor individually (e.g., parallel processing or processing by an object).

The computer program may be processed by one computer or may besubjected to distributed processing by plural computers. Further, thecomputer program may be transferred to a remote computer and executed.

Embodiments of the present invention are not limited to the embodimentsexplained above. Various modifications of the embodiments are possiblewithout departing from the spirit of the present invention.

1. An image processing apparatus comprising: an input to receive a signal representative of an original image; reducing means for reducing the original image at a reduction ratio and outputting a reduced image; and ΔΣ modulation means for applying, when predetermined signal processing is applied to a modulated image obtained by applying ΔΣ modulation to an image in a signal processing unit, the ΔΣ modulation to the reduced image, wherein a frequency characteristic of noise shaping by the ΔΣ modulation is a characteristic opposite to a frequency characteristic of the predetermined signal processing.
 2. An image processing apparatus comprising: an input to receive a signal representative of an original image; ΔΣ modulation means for applying, when predetermined signal processing is applied to a modulated image obtained by applying ΔΣ modulation to an image in a signal processing unit, the ΔΣ modulation to the image, wherein a frequency characteristic of noise shaping by the ΔΣ modulation is a characteristic opposite to a frequency characteristic of the predetermined signal processing, and wherein, when the signal processing unit interpolates a zero value and performing filtering by an LPF (Low Pass Filter) to thereby apply, as the predetermined signal processing, expansion processing for expanding an image at a predetermined expansion ratio, the frequency characteristic of the noise shaping by the ΔΣ modulation is a characteristic opposite to a frequency characteristic of the LPF, said apparatus further comprising reducing means for reducing the original image at a reduction ratio corresponding to the expansion ratio and outputting a reduced image, wherein the ΔΣ modulation means applies the ΔΣ modulation to the reduced image.
 3. An image processing method comprising: reducing an original image at a reduction ratio and outputting a reduced image; and applying, when predetermined signal processing is applied to a modulated image obtained by applying ΔΣ modulation to an image in a signal processing unit, the ΔΣ modulation to the reduced image, wherein a frequency characteristic of noise shaping by the ΔΣ modulation is a characteristic opposite to a frequency characteristic of the predetermined signal processing, and wherein the reducing and the applying are performed by a processing device.
 4. A non-transitory computer readable medium having stored thereon a computer program for causing a computer to function as: reducing means for reducing an original image at a reduction ratio and outputting a reduced image; and ΔΣ modulation means for applying, when predetermined signal processing is applied to a modulated image obtained by applying ΔΣ modulation to an image in a signal processing unit, the ΔΣ modulation to the reduced image, wherein a frequency characteristic of noise shaping by the ΔΣ modulation is a characteristic opposite to a frequency characteristic of the predetermined signal processing.
 5. An image processing apparatus comprising: a reducing unit to reduce an original image at a reduction ratio and outputting a reduced image; and a ΔΣ modulation unit configured to apply, when predetermined signal processing is applied to a modulated image obtained by applying ΔΣ modulation to an image in a signal processing unit, the ΔΣ modulation to the reduced image, wherein a frequency characteristic of noise shaping by the ΔΣ modulation is a characteristic opposite to a frequency characteristic of the predetermined signal processing, and wherein at least one of the ΔΣ modulation unit and the reducing unit are configured by hardware. 